1. Field of the Invention
The invention relates to an audio playback apparatus and, in particular, to an audio playback system switching between a speaker and an earphone.
2. Description of the Related Art
An audio amplifer is typically implemented with a D-type amplifier. A convnetional AB-type amplifier genereates a linear signal while a D-type amplifier genenrates a pluse width modulation (PWM) signal comprising a audio aignal and a PWM switching signal along with harmonics thereof. When the D-type amplifier operates, an output MOSFET thereof switches to a extremely low impedance state from a extremely high impedance state. Since the D-type amplifier stays in an active region only for a few nano seconds, output power consumption thereof is much lower than an AB-type amplifier. Such effective power amplification and conversion result in lower electrical power consumption and provide more applications such that a D-type amplifier has become a mainstream.
How to let a user selects a speaker or an earphone to play an audio signal processed by a D-type audio amplifier such that there is no intereference between the speaker and the earphone has bocome an important issue of D-type audio amplifier development. Accordingly, it is necessary to provide an audio playback apparatus capable of detecting whether a back-end output module is a speaker or an earphone and switching to the same to play the audio signal.